The present invention relates to a more efficient method of concentrating multicomponent liquid products, and more particularly, involves the retention of volatile constituents in the concentrated product through means of a closed system and the presence of secondary freezing agents.
Separation of individual components from multicomponent liquids by crystalization of one component and removal of the ice crystals is routinely used in analytical chemistry. For example, to separate water from a brine solution, small amounts of solution may be frozen and the ice crystals removed, leaving behind the concentrate. Crystalization is usually obtained by contacting the multicomponent liquid product and a nontoxic, nonpolar, low water soluble gas with low boiling point. Such liquid refrigerant gases include isobutane, freon, carbon dioxide, ethane and propane. Ice crystals are formed in the course of vaporization of the liquified refrigerant gas. A hydrate may also be formed between the water and the liquid refrigerant gas.
It is well known that a layer of the liquid to be treated adheres to the ice, and that the problem of its removal exists. One method for removal of this layer (see U.S. Pat. No. 3,525,230 to Smith) is washing with fresh water. However, if the wash water is returned in the solution being concentrated, the solution is diluted and additional concentration of solution is required. If wash water is not returned, there is a great loss of product, as well as volatile and nonvolatile constituents.
It is also well known that substantial entrainment of constituents from the liquid to be treated in ice crystals results due to fast freezing by direct contact between the liquid refrigerant gas and the liquid. Water crystal growth is faster than the diffusion of the molecules of admixtures from the ice crystals, and, therefore, these molecules become entrained in the crystal structure.
Another problem found in the traditional concentrating methods using liquid refrigerant gas is the loss of volatile constituents. These constituents, which in cases involving food products often comprise most of the flavor and scent, are trapped in the refrigerant gas and are lost when the gas is expelled. In addition, the presence of the volatile constituents in the liquid refrigeration gas can interfere with the operation of compressors, valves and other elements of the system.
Another method of concentrating multicomponent liquids involves vacuum vaporization and formation of ice due to temperature reduction in the course of such vaporization. The ice is collected and melted. The disadvantage of this process modification is that almost all volatile constituents will be lost if present in the treated liquid.
It is an object of the present invention to provide a more efficient method for concentrating multicomponent liquids while retaining volatile and nonvolatile constituents in the concentrate.